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采用基于广义梯度近似的投影缀加平面波(projector augmented wave)赝势和具有三维周期性边界条件的超晶胞模型,用第一性原理计算方法,计算并分析了Pd在CeO2(111)面上不同覆盖度时的吸附能,价键结构和局域电子结构.考虑了单层Pd和1/4单层Pd两种覆盖度吸附的情况.结果表明:1)在单层吸附时,Pd的最佳吸附位置是O的顶位偏向Ce的桥位;在1/4单层吸附时,Pd最易在O的桥位偏向次层O的顶位吸附.2)单层覆盖度吸附时,吸附原子Pd之间的作用较强;1/4单层覆盖度吸附时,同层吸附的Pd之间的几乎没有相互作用.同时在低覆盖度吸附时,Pd和CeO2衬底的相互作用较高覆盖度时强.3)Pd的吸附只对其近邻的衬底原子结构有明显影响.4)Pd在CeO2衬底上吸附后,Pd和CeO2衬底的活性增强,并可能在Pd与CeO2界面处形成活性中心.以上结果有助于人们对三元催化剂中Pd与CeO2的协同作用机理的理解.
Based on the generalized gradient approximation of the projector augmented wave pseudopotentials and the supercell cell model with three-dimensional periodic boundary conditions, a first-principles calculation method was used to calculate and analyze the Pd on the CeO2 (111) surface The adsorption energy, valence bond structure and local electronic structure with different coverage were considered. The adsorption of Pd on single layer and Pd on 1/4 layer were considered. The results showed that: 1) The best position for adsorption is the top position of O, which is close to the bridge site of Ce. At the time of 1/4 monolayer adsorption, Pd is most likely to be adsorbed on the top position of O in the bridge position of O. (2) The interaction between Pd and CeO2 is stronger than that between Pd and CeO2, and there is almost no interaction between Pd adsorbed on the same layer and the Pd adsorbed on the Pd substrate. Pd and CeO2 only have strong influence on the atomic structure of the substrate.4) After the Pd adsorbed on the CeO2 substrate, the activity of Pd and CeO2 substrate is enhanced, and the Pd and CeO2 The active site formed at the interface.The above results help to understand the synergistic mechanism of Pd and CeO2 in the three-way catalyst.